1. Field of the Invention
The present invention relates to a method for manufacturing trichlorosilane which is a raw material of polycrystalline silicon.
The present application claims priority on Japanese Patent Application No. 2011-143123, filed on Jun. 28, 2011, the content of which is incorporated herein by reference.
2. Background Art
High-purity polycrystalline silicon used as a semiconductor material is mainly manufactured by the following method (the Siemens process). At first, trichlorosilane (SiHCl3:TCS) and hydrogen (H2) are mixed so as to obtain a mixed gas of the raw materials. The mixed gas is introduced to a reactor so as to be brought in contact with heated silicon rods. Polycrystalline silicon is deposited on the surfaces of the silicon rods by reactions due to hydrogen reduction and thermal decomposition of trichlorosilane at high temperatures.
In this manufacturing of the high-purity polycrystalline silicon, gases exhausted from the reactor contain unreacted trichlorosilane, unreacted hydrogen, silicon tetrachloride (SiCl4:STC), hydrogen chloride, and the like as a byproduct. Therefore, the exhausted gases after the reaction are cooled so as to obtain a non-condensed component including hydrogen and a condensate including silanes. Then, hydrogen is recovered from the non-condensed components, and the condensate is distilled so as to recover trichlorosilane and silicon tetrachloride.
Subsequently, silicon tetrachloride obtained through the distillation is used to react with metallurgical grade silicon and hydrogen, and the reaction gas is cooled so as to obtain a condensate. The obtained condensate is distilled and refined so as to obtain trichlorosilane. Trichlorosilane obtained through this process is reused as a raw material for polycrystalline silicon deposition.
In Japanese Unexamined Patent Application, First Publication No. H10-29813, a technique is disclosed in which silicon particles (metallurgical grade silicon), silicon tetrachloride, and hydrogen are reacted with each other in a fluidized bed at high temperatures in the presence of a catalyst containing copper silicide so as to convert silicon tetrachloride into trichlorosilane.
In addition, in the gas produced by this conversion reaction, unreacted silicon tetrachloride and unreacted hydrogen are contained together with the produced trichlorosilane. Powder of metallurgical grade silicon used as the raw material, and metal chlorides produced through reactions with other impurities (Fe, Al, Ti, Ni, and the like) contained in metallurgical grade silicon are also contained in the gas. Among the metal chlorides, aluminum chloride (AlCl3) has a relatively low sublimation point; and therefore, aluminum chloride becomes a cause of clogging or corrosion of pipes. Therefore, aluminum chloride and the like are extracted and exhausted from a column bottom of a distillation column when trichlorosilane is recovered from a conversion reaction gas. In addition, in order to prevent clogging of pipes between a converter to the distillation column, the concentration of aluminum contained in metallurgical grade silicon of the raw material is controlled to be lower than a predetermined amount (refer to Japanese Unexamined Patent Application, First Publication No. 2006-1804).
In the method for manufacturing trichlorosilane using metallurgical grade silicon as the raw material according to the conventional art, as disclosed in Japanese Unexamined Patent Application, First Publication No. 2006-1804, the concentration of aluminum in metallurgical grade silicon needs to be strictly controlled. However, there is a problem in that reducing of impurities in metallurgical grade silicon causes an increase in manufacturing costs of the raw material and a restriction of varieties of the raw material.
The present invention is designed to solve the above-mentioned problems. An object of the present invention is to provide a method for manufacturing trichlorosilane which is capable of efficiently removing aluminum chloride without being restricted by the concentration of impurities in the raw material of metallurgical grade silicon and without causing clogging of pipes and the like.